With the increased recording density of hard disk drives, the distance between a magnetic disk serving as a recording medium and a head for recording and reproducing information has become almost nil as they approach contact with each other. The magnetic disk surface is provided with a carbon protective film and a lubricant film (lubricant layer) to diminish abrasion caused by contact with the head or sliding of the head thereon, and to prevent contamination of the magnetic disk surface. The two layers protect the surface of the magnetic disk. In particular, the lubricant layer provided on the top must have various properties, such as long-term stability, chemical resistance, friction properties, and heat resistance.
Fluoropolyethers have often been used as lubricants for magnetic disks. However, fluoropolyether-based lubricants have low resistance to Lewis acid. Due to contact with the magnetic head, etc., the main chain is cut by alumina (Al2O3) contained in the magnetic head member, reducing the molecular weight of the lubricant. Subsequently, the transfer (pickup) of the lubricant with a reduced molecular weight to the magnetic head occurs, thereby reducing lubrication, and thus causing the hard disk drive to crash.
In order to address these problems, some techniques have been proposed in which a high electron-donating functional group is introduced into the fluoropolyether molecule, and the functional group comes into contact with an active alumina part in the magnetic head to induce an interaction, thereby inactivating alumina.
For example, PTL 1 proposes a fluoropolyether having a cyclophosphazene group at both terminals of the molecule. However, in a lubricant containing the compound disclosed in PTL 1, almost all highly electron-donating functional groups present in the lubricant molecule bind to the carbon protective film of a magnetic disk. Thus, the functional groups cannot come into contact with an active alumina part, and cannot inactivate active alumina.
PTL 2 discloses a fluoropolyether having two hydroxyl groups at both terminals of the molecule. The terminal hydroxyl groups of the compound disclosed in PTL 2 have decomposition resistance. However, almost all functional groups bind to the carbon protective film, as in PTL 1; therefore, alumina causes decomposition, as in PTL 1, and pickup occurs.